The invention relates to homogeneous catalysts for the metathesis of olefins, including functionalized olefins, a process that is defined as the redistribution of alkylidene moieties in a mixture of olefins to give all possible olefins. The simplest example is EQU 2R'CH.dbd.CHR.revreaction.R'CH.dbd.CHR'+RCH.dbd.CHR
The reaction proceeds by addition of an olefin to a metal-carbon double bond (M=CHR, a metal-alkylidene complex) to give a metal-lacyclobutane ring, which then releases an olefin to reform a metal-alkylidene complex.
Prior to this invention, there has been no report of a well-characterized tungsten or molybdenum catalyst for the metathesis of functionalized olefins. The tungsten catalyst system that is known consists of WCl.sub.6 activated by a stoichiometric quantity of a tetraalkyltin reagent at 110.degree. C. (J. C. Mol J. Molec. Catal. 15 (1982) 35; J. C. Mol Chem. Tech. 13 (1983) 250; R. H. A. Bosma, G. C. N. Van den Aardweg and J. C. Mol J. Organometal. Chem. 255 (1983) 159). Variations are known such as the catalyst system consisting of WOCl.sub.4 activated by Ti(.eta..sup.5 --C.sub.5 H.sub.5).sub.2 (CH.sub.3).sub.2 (J. Tsuji and S. Hashiguchi Tet. Lett. 21 (1980) 2955), WCl.sub.6 activated with BEt.sub.3 (R. Nakamura, S. Fukuhara, S. Matsumoto and K. Komatsu (Chem. Lett. (1976) 253; R. Nakamura, S. Matsumoto and E. Echigoya Chem. Lett. (1976) 1019), Mo(OEt).sub. 2 Cl.sub.3 activated by BEt.sub.3 (Nakamura) and WCl.sub.6 activated by Al.sub.2 Me.sub.3 Cl.sub.3 (Nakamura).
A second catalyst system that appears to be more active and long-lasting than tungsten-based systems is a heterogeneous catalyst prepared by depositing Re.sub.2 O.sub.7 on silica or alumina and activating it with tetraalkyltin reagents (see articles by Mol above). It is active at room temperature.
A typical olefin of interest for testing catalysts is an ester of oleic acid, owing to the great abundance of oleic acid in natural oils such as olive oil (oleic acid=cis--CH.sub.3 (CH.sub.2).sub.7 CH.dbd.CH(CH.sub.2).sub.7 CO.sub.2 H). The characteristic of all catalyst systems known so far is that they are relatively slow, sometimes unselective, sometimes destructive due to their Lewis acidic nature, and not long-lasting. The best catalyst system to date is a heterogeneous rhenium catalyst prepared on silica/alumina mixtures (X. Xiaoding and J. C. Mol J. Chem. Soc. Chem. Comm. (1985) 631). Maximum activity to date consists of metathesis of about 60 equivalents of methyl oleate to the equilibrium mixture in one hour. Thereafter, the catalyst system is inactive, thereby limiting the practicality of these relatively expensive (Re) catalysts.
It would be desirable to provide a catalyst for metathesizing functionalized olefins at a molecular level that would be based on cheaper metals (Mo, W) and that would be more active and longer lived. Such catalysts can be utilized as homogeneous catalysts or could be attached covalently to inorganic (e.g. silica) or organic (e.g. polystyrene) supports to yield analogous heterogeneous catalysts.